Momentum and Collisions Elastic and Inelastic Collisions

Collisions When two objects come together In some collisions, the objects stick together Perfectly Inelastic In other collisions, the objects separate Elastic Total kinetic energy is usually not conserved because kinetic energy is converted to internal energy as the objects deform

Perfectly Inelastic Collisions Perfectly inelastic collision – a collision in which two objects stick together and move with a common velocity after colliding An arrow sticking into a target Mass of the first object * initial velocity of the first object + mass of the second object * initial velocity of the second object equals the final velocity * the sum of the two object’s masses m1v1,i + m2v2,i = (m1+m2)vf

Perfectly Inelastic Collisions

Perfectly Inelastic Collisions Remember to assign positive and negative values based on direction Kinetic energy is not constant in perfectly inelastic collisions

Elastic Collisions Elastic collision – a collision in which the total momentum and total kinetic energy remain constant m1v1,i + m2v2,i = m1v1,f + m2v2,f ½m1v1,i2 + ½m2v2,i2 = ½m1v1,f2 + ½m2v2,f2

Elastic Collisions

Inelastic Collisions Most collisions are neither elastic nor perfectly inelastic Fall into a third category Inelastic collisions – the colliding objects bounce and move separately after collision, but total kinetic energy decreases

Collisions